However, LiDAR cannot see the road when snow obstructs it from view — like during inclement weather or in high-density traffic, according to a Ford statement. The same is true when the sensor lens is covered by snow, grime or debris.

The solution Ford and U-M are working on involves high-resolution 3-D maps — complete with information about the road and what's above it, including road markings, signs, geography, landmarks and topography. U-M researchers have developed these maps and Ford's test vehicles are equipped with them.

"Maps developed by other companies don't always work in snow-covered landscapes. The ones developed by Ford and the University of Michigan do," Eustice said. "The maps we create contain useful information about the 3-D environment around the car, allowing it to localize even with a blanket of snow covering the ground."

The autonomous vehicles create the maps while driving the test environment in favorable weather. Technologies automatically annotate features like traffic signs, trees and buildings later. Then, when the vehicles cannot see the ground, they detect above-ground landmarks to pinpoint themselves on the map, which they then use to drive successfully.

"The vehicle's normal safety systems, like electronic stability control and traction control, which often are used on slippery winter roads, worked perfectly alongside the autonomous driving software," McBride said. "We eventually want our autonomous vehicles to detect deteriorating conditions, decide whether it's safe to keep driving, and if so, for how long."

As the beautiful old car cruised in almost perfect silence under the guidance of its automatic controls, Duncan tried to see something of the terrain through which she was passing... Duncan could count at least 20 vehicles of different types and even though they were all moving in the same direction, the spectacle was somewhat alarming...
(Read more about Arthur C. Clarke's autonomous cars)